Why do we yawn?

Professor John Miller, School of Biological Sciences, answers the age-old question: Why do we yawn?

Man yawning

Professor John Miller, School of Biological Sciences, answers:

Yawning is induced by tiredness, reduced activity, and boredom. It is also contagious, in both humans and animals. It’s involuntary, and foetuses as early as 11 weeks sometimes yawn.

Yawning involves a complex reflex that uses a large number of motor systems, including opening of the mouth and jaws and a long, deep inflation of the lungs. Other secondary motor activities are also a part of yawning, such as opening of the ear canals, closing the eyes, and stretching of the arms and back.

It’s not just for show though. Yawning serves a useful purpose by popping open the small air sacs in the lungs that slowly collapse with long-term quiet, restful breathing, hence, the link to sleep and boredom when breathing tends to be subdued and shallow. A good yawn inflates the air sacs in the lungs and improves the pickup of oxygen and release of carbon dioxide.